The present invention relates to an absorption refrigerator and, more particularly, to an improvement in an absorber of the absorption refrigerator.
In general, an absorption refrigerator comprises an absorber, an evaporator, a condenser, a low temperature generator, a high temperature generator, a heat exchanger and pipings with pumps for fluidly connecting them. The evaporator has a tube bank therein in which water flows. Water as a refrigerant is sprayed outside the tube bank to cool the water inside the tube bank by latent heat of evaporation. The cooled water is supplied as a coolant to a cooler or the like. Steam or vapor generated in the evaporator flows into the absorber and it is absorbed into an absorbent, such as lithium bromide, which is sprayed on the tube outer surfaces of a tube bank arranged in the absorber. Absorption heat generated at this time is picked up by cooling water flowing in the tube bank. The absorbent which absorbed vapor in the absorber is lowered in concentration and it also is weakened in absorbability. Therefore, the absorbent is sent to the high temperature generator and the low temperature generator to heat and concentrate there after pre-heating by passing through the heat exchanger. Generally, heat generated by burning gas, oil, etc. is used as a heat source of the high temperature generator. The vapor generated in the high temperature generator is used as a heat source of the low temperature generator. The vapor generated in the high temperature generator and the low temperature generator is cooled finally by cooling water in the condenser to form a condensate. The condensed water is supplied to the evaporator as an evaporation medium. The absorber is the most important component of all the components of the absorption refrigerator from the point of view of performance of the absorption refrigerator.
Both the evaporator and the absorber are kept to a low pressure. Therefore, in the evaporator, the coolant, such as water flowing in the tube bank can be cooled with latent heat by evaporating an evaporation medium, such as water sprayed on the outer surface of the tube bank, as mentioned above. The absorber, in general, comprises a tube bank in which tubes are arranged in a zigzag fashion or in a lattice fashion, and a spray device for spraying absorbent on the outer surfaces of the tube bank. In general, a lithium bromide solution is used as the absorbent, and is sprayed on the outer surfaces of the heat-exchange or heat-conductive tube bank. The vapor pressure of the lithium bromide solution is much smaller than that of water, the vapor flowing from the evaporator into the absorber being absorbed depending on the pressure difference therebetween. In this case, the temperature of the absorbent is raised by absorption heat, and so the absorbent is cooled by causing coolant, such as water, to flow in the tube bank.
In order to improve the performance of the absorption refrigerator, it is necessary to increase the effective pressure difference between the vapor pressure in the evaporator and the vapor pressure in the absorber in view of the above-mentioned principle of absorption cycle operation. Therefore, first, it is necessary to increase the pressure difference available to absorb the vapor in the absorber by decreasing the flow resistance (pressure loss) of the vapor in the tube banks of the evaporator and the absorber. Secondly, it is necessary to increase the absorption heat conduction characteristic in the absorber. There are three ways for carrying this out. One of them is by forming fins on the surfaces of heat exchange tubes in the manner disclosed in JP A 63-6363 (1988) to increase the absorption heat conductive characteristic of a single tube of the tube bank, thereby increasing the heat conductive area and increasing the amount of absorbent retained on the surfaces. Another is a method of preventing uncondensed gas, such as air, to stagnate, which uncondensed gas then becomes a conductive resistance on the vapor side. And another is a way to reduce the number of conductive tubes which are not to be used for absorption by supplying absorbent evenly over each heat exchange tube in the absorber. An example of a prior proposal for increasing the performance is disclosed in JP B 58-19021 (1983) in which an evaporator has a heat exchange tube bank formed in lattice form of small pitch at an upstream side of the vapor flow and in a zigzag form of a larger pitch at the downstream side at which a larger amount of the vapor flows, and an absorber also has a heat exchange tube bank formed in a zigzag form of large pitch at an upstream side of the vapor flow at which a larger amount of vapor flows and in lattice form of small pitch at a downstream side of the vapor flow, whereby the flow resistance is made uniform in the tube banks. Another example is in JP A 62-155482 in which partitions are provided in an absorber, which partitions are parallel with the outermost tube rows, whereby gas is prevented from becoming stagnant and is extracted from the tube bank.